The equipment for the cleaning of the above mentioned glass surfaces, usually included as original equipment in motor vehicles, comprises, among other items as is well known, a pump which is adapted to a reservoir containing cleaning liquid and which pumps this liquid through tubing and sprays it over the said surfaces at a rate and with a pressure adapted to the needs of each particular application.
These pumps are driven by a d.c. electric motor which is connected through the corresponding protection and control members to the vehicle battery. Under these conditions, the pump is set running by way of the said control members disposed inside the vehicle and operated by the driver depending on the driving conditions of the vehicle.
From the foregoing, it has appeared necessary, for safety reasons, to keep a check over the amount of cleaning liquid available in the said auxiliary reservoir. This control consists normally of an optical and/or acoustical alarm signal, which is disposed in an appropriate place in the vehicle interior and which is operated by a device associated with the cleaning liquid reservoir.
In this way, the said signal indicates, on being activated, that the level of cleaning liquid in the reservoir has dropped to the preset minimum level.
The known embodiments of devices for controlling the level of cleaning liquid in the reservoir:
include devices which may be coupled, independently of the pump, to the cleaning liquid reservoir and which are operatively based on the action of a float on a reed relay; and also
devices which may be integrated in the structure of the pump itself.
Among the latter, there may be mentioned the device disclosed in Spanish patent P.9000819 for "A control device for liquid levels", which operates by means of a continuity sensor which detects the presence of cleaning liquid in terms of the passage of a weak electric current through said liquid and which is connected to a reversing circuit and to an amplifying circuit which operates on the above mentioned signalling members.
Generally speaking, the known embodiments of such control devices integrated in the pump structure suffer from drawbacks relating to the high production costs and poor stability of the signal when the cleaning liquid level is substantially below the level chosen as limit for activation thereof.